For a magnetic recording medium particularly a magnetic recording medium such as a magnetic tape, a magnetic disk or a magnetic sheet which is required to have particularly tough durability for higher density recording, it is necessary to simultaneously improve surface smoothness and running durability, thereby improving electromagnetic characteristics.
However, the conventionally used magnetic recording medium has not been able to fully respond to the above requirements for higher density recording. In fact, it is very important for a magnetic disk and the like with higher density recording that the surface of a magnetic layer be smoothed and the ferromagnetic particles be homogeneously dispersed in the magnetic layer. However, such means of making magnetic particles finer, reinforcing the smoothing treatment such as calendaring treatment and improving the dispersibility of a magnetic coating composition, which have been done so far, are not enough to give the magnetic layer sufficient durability. In actuality, a magnetic layer is made thinner and thinner with higher density recording of a magnetic recording medium.
In the past, as a means to improve running durability of a magnetic layer, various lubricating agents have been added to the magnetic layer. However, when a magnetic layer is made thinner and thinner, sufficient running durability cannot be obtained. Even with the addition of a lubricating agent into the magnetic layer the surface of the magnetic layer is easily damaged by the magnetic head while the magnetic recording medium is running in a magnetic recording apparatus and even slight unevenness on the surface of a support such as a polyester film affects the surface of the magnetic layer, thereby deteriorating electromagnetic properties.
In this connection, the inventors of the present invention made thorough studies to solve the above problems of the conventional art occurring with reduction of the thickness of a magnetic layer of a reduction of the thickness of a magnetic layer of a magnetic recording medium, and as a result thereof, the inventors have found unexpected facts and have attained the present invention.